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Comparison of irrational numbers - class-IX

Description: comparison of irrational numbers
Number of Questions: 51
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Tags: rational and irrational numbers maths exponents
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Compare the following pairs of surds. $\sqrt[8]{80}, \sqrt[4]{40}$    

  1. $\sqrt[8]{80} < \sqrt[4]{40}$

  2. $\sqrt[8]{80} \neq \sqrt[4]{40}$

  3. $\sqrt[8]{80} = \sqrt[4]{40}$

  4. $\sqrt[8]{80} > \sqrt[4]{40}$


Correct Option: A
Explanation:

   $\sqrt[8]{80}, \sqrt[4]{40}$
$={80}^{\frac{1}{8}}, {40}^{\frac{1}{4}}$
$={80}^{\frac{1}{8}}, {40}^{\frac{2}{8}}$
$={80}^{\frac{1}{8}}, {1600}^{\frac{1}{8}}$
Now,
   $80<1600$
$=>{80}^{\frac{1}{8}}<{1600}^{\frac{1}{8}}$
$=>\sqrt[8]{80}< \sqrt[4]{40}$

Which among the following numbers is the greatest?
$\displaystyle 0.07+\sqrt{0.16},\sqrt{1.44},1.2\times 0.83,1.02-\frac{0.6}{24}$

  1. $\displaystyle \sqrt {1.44}$

  2. $\displaystyle 0.07+\sqrt{0.16}$

  3. $1.2\times 0.83$

  4. $1.02-\dfrac{0.6}{24}$


Correct Option: A
Explanation:
$\Rightarrow 0.07+\sqrt{0.16}=0.07+0.4=0.47$
$\Rightarrow \sqrt{1.44}=1.2$
$\Rightarrow 1.2 \times 0.83 = 0.996$
$\Rightarrow 1.02-\cfrac{0.6}{24}=1.02-\cfrac {6}{240}=1.02-0.025=0.995$
$ \therefore$ The greatest number is $1.2$ i.e. $\sqrt {1.44}$

State whether the following equality is true or false:

$\displaystyle \frac{2\sqrt{3}}{\sqrt{5}} = $$\displaystyle \frac{2\sqrt{15}}{\sqrt{5}}$

  1. True

  2. False


Correct Option: B
Explanation:

Rationalizing factor of  $\displaystyle \frac{2\sqrt{3}}{\sqrt{5}}$ is $\sqrt{5}$


$\therefore \displaystyle \frac{2\sqrt{3}}{\sqrt{5}}$  $=\displaystyle \frac{2\sqrt{3}\times \sqrt{5}}{\sqrt{5}\times \sqrt{5}}$

$= \dfrac{2\sqrt{15}}{5}$

Determine the order relation between the following pairs of ratios.

$\displaystyle \frac{3\sqrt{3}}{2\sqrt{2}}, \frac{2\sqrt{2}}{3\sqrt{3}}$

  1. $\displaystyle \frac{3\sqrt{3}}{2\sqrt{2}} > \frac{2\sqrt{2}}{3\sqrt{3}}$

  2. $\displaystyle \frac{3\sqrt{3}}{2\sqrt{2}} < \frac{2\sqrt{2}}{3\sqrt{3}}$

  3. Cannot be determined

  4. None of These


Correct Option: A
Explanation:

$\dfrac{3\sqrt{3}}{2\sqrt{2}}=\dfrac{3\times 1.73214}{2\times 1.41429} = \dfrac{5.19642}{2.85828}
=1.82151$
$\dfrac{2\sqrt{2}}{3\sqrt{3}}=\dfrac{2\times 1.41429}{3\times 1.73214}=\dfrac{2.85828}{5.19642}=0.55004$
$\therefore \dfrac{3\sqrt{3}}{2\sqrt{2}} >\dfrac{2\sqrt{2}}{3\sqrt{3}}$

Compare the following pairs of surds $\sqrt[8]{12}, \sqrt[4]{6}$

  1. $\sqrt[8]{2} < \sqrt[4]{6}$

  2. $\sqrt[8]{8} < \sqrt[4]{6}$

  3. $\sqrt[8]{12} < \sqrt[4]{6}$

  4. $\sqrt[8]{12} < \sqrt[4]{4}$


Correct Option: C

Compare the following pair of surds:

$\sqrt[3]{6}, \sqrt[4]{8}$

  1. $\sqrt[3]{6} > \sqrt[4]{8}$

  2. $\sqrt[3]{6} > \sqrt[4]{4}$

  3. $\sqrt[3]{6} > \sqrt[3]{8}$

  4. $\sqrt[3]{4} > \sqrt[4]{8}$


Correct Option: A

Arrange the following in ascending order of magnitude: 

$\displaystyle \sqrt[3]{4}, \sqrt[4]{5}, \sqrt{3}$ 

  1. $\displaystyle \sqrt[4]{5} < \sqrt[3]{4} < \sqrt{3}$

  2. $\displaystyle \sqrt[4]{5} > \sqrt[3]{4} > \sqrt{3}$

  3. $\displaystyle \sqrt[4]{5} > \sqrt[3]{4} < \sqrt{3}$

  4. $\displaystyle \sqrt[4]{5} < \sqrt[3]{4} > \sqrt{3}$


Correct Option: A

What is the least value of $a$ in $ \displaystyle\frac{\sqrt 2+\sqrt 3}{\sqrt{2+3}} < a$?

  1. $1$

  2. $2$

  3. $3$

  4. $4$


Correct Option: B
Explanation:
$\dfrac { \sqrt { 2 } +\sqrt { 3 }  }{ \sqrt { 2+3 }  } =\dfrac { \sqrt { 2 } +\sqrt { 3 }  }{ \sqrt { 5 }  } =\dfrac { (\sqrt { 2 } +\sqrt { 3 } )\times \sqrt { 5 }  }{ 5 } =\dfrac { 7.02 }{ 5 } \\ =1.40$
$\Rightarrow 1.40<a$
So, least integer value of $a$ is $2$.
Hence, option B is correct.

Which of the following is the greatest?

  1. $\sqrt 2$

  2. $\sqrt 3$

  3. $\sqrt 4$

  4. $\sqrt 5$


Correct Option: D
Explanation:

$\sqrt 5$ > $\sqrt 4$ > $\sqrt 3$ > $\sqrt 2$


So, option D is correct.

The greatest among $\displaystyle \sqrt[6]{3}$, $\displaystyle \sqrt{2}$, $\displaystyle \sqrt[3]{4}$, $\displaystyle \sqrt[4]{5}$ is--

  1. $\displaystyle \sqrt[6]{3}$

  2. $\displaystyle \sqrt{2}$

  3. $\displaystyle \sqrt[3]{4}$

  4. $\displaystyle \sqrt[4]{5}$


Correct Option: C
Explanation:

$\displaystyle \therefore $ $\displaystyle \sqrt[6]{3}$ = $\displaystyle \left ( 3 \right )^{\dfrac{1}{6}}$ = $\displaystyle \left ( 3^{2} \right )^{\dfrac{1}{12}}$ = $\displaystyle \left ( 9 \right )^{\dfrac{1}{12}}$
$\displaystyle \sqrt{2}$ = $\displaystyle \left ( 2 \right )^{\dfrac{1}{2}}$ = $\displaystyle \left ( 2^{6} \right )^{\dfrac{1}{12}}$ = $\displaystyle \left ( 64 \right )^{\dfrac{1}{12}}$
$\displaystyle \sqrt[3]{4}$ = $\displaystyle \left ( 4 \right )^{\dfrac{1}{3}}$ = $\displaystyle \left ( 4^{4} \right )^{\dfrac{1}{12}}$ = $\displaystyle \left ( 256 \right )^{\dfrac{1}{12}}$

$\sqrt[4]{5}=(5)^{\dfrac{1}{4}}=(5^{3})^{\dfrac{1}{12}}=(125)^{\dfrac{1}{12}}$
$\displaystyle \therefore $ The greatest number is $\displaystyle \left ( 256 \right )^{\dfrac{1}{12}}$ = $\displaystyle \sqrt[3]{4}$

Which of the following is smallest?

  1. $ \displaystyle \sqrt[4]{5} $

  2. $ \displaystyle \sqrt[5]{4} $

  3. $ \displaystyle \sqrt{4} $

  4. $ \displaystyle \sqrt{3} $


Correct Option: B
Explanation:

Since, fifth root of four is smallest.

Option $B$ is correct.

Which one of the following is the smallest surd?

  1. $\sqrt 4$

  2. $\sqrt {27}$

  3. $\sqrt 9$

  4. $\sqrt 5$


Correct Option: A
Explanation:
As we know, $4 < 5 < 9 < 27$
So, $\sqrt 4$ < $\sqrt 5$ < $\sqrt 9$ < $\sqrt {27}$
Hence, the answer is $\sqrt{4}$.

If $p=\sqrt{32}-\sqrt{24}$ and $q=\sqrt{50}-\sqrt{48}$, then:

  1. $p< q$

  2. $p> q$

  3. $p=q$

  4. $p\le q$


Correct Option: B
Explanation:

$p= \sqrt{32} - \sqrt{24}$

$p= 5.656-4.898 = 0.758$

$q = \sqrt{50} + \sqrt{48}$

$q= 7.071- 6.928 = 0.089$

$\therefore p> q$

If $x=\sqrt{2}+1, y=\sqrt{17}-\sqrt{2}$, then .............

  1. $x< y$

  2. $x>y$

  3. $x=y$

  4. $x\ge y$


Correct Option: A
Explanation:

$\sqrt{2} =1.414$

$\sqrt{17} =4.123$

Hence,

$x = \sqrt{2}+1 =1.414+1 = 2.414$

$ y= \sqrt{17} -\sqrt{2} =4.123- 1.414 = 2.709$

Hence , $x<y$

$\sqrt{11}-\sqrt{10}$ $\Box$ $ \sqrt{12}-\sqrt{11}$

  1. $<$

  2. $>$

  3. $=$

  4. cannot be determined


Correct Option: B
Explanation:

$\sqrt{11} =3.316$

$\sqrt{10} =3.162$

$\sqrt{12} =3.464$

Hence,

$\sqrt{11} -\sqrt{10} =3.316-3.162 = 0.154$

$\sqrt{12} -\sqrt{11} =3.464-3.316 = 0.148$

Hence , $\sqrt{11} -\sqrt{10} >\sqrt{12} -\sqrt{11}$

Which among the following numbers is the greatest?
$\displaystyle \sqrt[3]{4},\sqrt{2},\sqrt[6]{13},\sqrt[4]{5}$

  1. $\displaystyle \sqrt[3]{4}$ is the greatest

  2. $\sqrt{2}$ is the greatest

  3. $\sqrt[6]{13}$ is the greatest

  4. $\sqrt[4]{5}$ is the greatest


Correct Option: A
Explanation:

LCM of $3, 6, 4 = 12$

So, raising each given number to power $12$.
$\Rightarrow \sqrt[3]{4}=(4)^{1/3}=(4^{1/3})^{12}=4^{4}=256$
$\Rightarrow \sqrt{2}=(2)^{1/2}=(2^{1/2})^{12}=2^{6}=64$
$\Rightarrow \sqrt[6]{13}=(13)^{1/6}=(13^{1/6})^{12}=13^{2}=169$
$\Rightarrow \sqrt[4]{5}=(5)^{1/4}=(15^{1/4})^{12}=5^{3}=125$

$\therefore \sqrt[3]{4}$ is the greatest.

If $x=\sqrt{7}-\sqrt{5}, y=\sqrt{13}-\sqrt{11}$, then:

  1. $x=y$

  2. $x> y$

  3. $x< y$

  4. $x\ge y$


Correct Option: B
Explanation:

$x = \sqrt{7}-\sqrt{5}$

$= 2.64 – 2.23= 0.41$

$y=  \sqrt{13}-\sqrt{11}$

$= 3.60- 3.31 = 0.29$

$Hence, x> y$

If $A=\sqrt{7}-\sqrt{6}$ and $B=\sqrt{6}-\sqrt{5}$, then identify the true statement.

  1. $A> B$

  2. $A=B$

  3. $A< B$

  4. $A\ge B$


Correct Option: C
Explanation:
$A=\sqrt{7}-\sqrt{6}\Rightarrow \dfrac{1}{A}=\dfrac{\sqrt{7}+\sqrt{6}}{(\sqrt{7}-\sqrt{6})(\sqrt{7}+\sqrt{6})}$
$\Rightarrow \boxed{\dfrac{1}{A}=\sqrt{7}+\sqrt{6}}$
$\boxed{\dfrac{1}{B}=\sqrt{6}+\sqrt{5}}$
As $\sqrt{7} > \sqrt{5}\Rightarrow \dfrac{1}{A} > \dfrac{1}{B}$
$\Rightarrow \boxed{B > A}$

The smallest between $\sqrt{17} - \sqrt{12}$ and $\sqrt{11} - \sqrt{6}$ is _________.

  1. $\sqrt{17} - \sqrt{12}$

  2. $\sqrt{11} - \sqrt{6}$

  3. Both are equal

  4. Can't be determined


Correct Option: A
Explanation:

$\sqrt{17} \approx 4.123$

$\sqrt{12} \approx 3.464$
$\sqrt{11} \approx 3.316$
$\sqrt{6} \approx 2.449$

$\Rightarrow \sqrt{17} - \sqrt{12} = 0.659$
$\Rightarrow \sqrt{11} - \sqrt{6} = 0.867$

Hence, $\sqrt{17}-\sqrt{12}$ is smaller.

The smallest of $\sqrt [ 3 ]{ 4 } , \sqrt [ 4 ]{ 5 } , \sqrt [ 4 ]{ 6 } , \sqrt [ 3 ]{ 8 } $ is:

  1. $\sqrt [ 3 ]{ 8 } $

  2. $\sqrt [ 4 ]{ 5 } $

  3. $\sqrt [ 3 ]{ 4 } $

  4. $\sqrt [ 4 ]{ 6 } $


Correct Option: B
Explanation:
$\sqrt[3]{4}=\sqrt[12]{44}=\sqrt[12]{256}$
$\sqrt[4]{6}=\sqrt[12]{5^3}=\sqrt[12]{125}$
$\sqrt[4]{6}=\sqrt[12]{6^{3}}=\sqrt[12]{216}$
$\sqrt[3]{8}=\sqrt[12]{8^{4}}=\sqrt[12]{64^{2}}$
As $'125'$ is smallest
$\therefore \boxed{4\sqrt{5}}$ is smallest

Let x and y be rational and irrational numbers, respectively, then x + y necessarily an irrational number.


State True or False.

  1. True

  2. False


Correct Option: A
Explanation:

Yes.

Let x $= 21, y =\sqrt{2}$ be a rational number
Now $x+y=21 +\sqrt{2}=21+1.4142....=22.4142....$ , which is non-terminating and non-recurring. Hence x+y is irrational.

If $A=\sqrt [ 3 ]{ 3 } , B=\sqrt [ 4 ]{ 5 } $, then which of the following is true?

  1. $A=\cfrac{3}{5}B$

  2. $A< B$

  3. $A> B$

  4. $A={B}^{4/5}$


Correct Option: B
Explanation:
$A=3^{\dfrac{1}{3}}=\sqrt[12]{34}=\sqrt[12]{81}$
$B=5^{\dfrac{1}{4}}=\sqrt[12]{5^{3}}=\sqrt[12]{125}$
As $125 > 81$
$\Rightarrow \boxed{B > A}$

The descending order of the surds $\sqrt[3]{2} , \sqrt[6]{3} , \sqrt[9]{4}$ is _________.

  1. $\sqrt[9]{4} , \sqrt[6]{3} , \sqrt[3]{2}$

  2. $\sqrt[9]{4} , \sqrt[3]{2} , \sqrt[6]{3}$

  3. $\sqrt[3]{2} , \sqrt[6]{3} , \sqrt[9]{4}$

  4. $\sqrt[6]{3} , \sqrt[9]{4} , \sqrt[3]{2}$


Correct Option: C
Explanation:

$\sqrt[3]{2} \approx 1.26$

$\sqrt[6]{3} \approx 1.201$
$\sqrt[9]{4} \approx 1.166$

$\therefore$ Ascending order is $\sqrt[9]{4} < \sqrt[6]{3} < \sqrt[3]{2}$

Which of the following is smallest ?

  1. $\sqrt[4]{5}$

  2. $\sqrt[5]{4}$

  3. $\sqrt{4}$

  4. $\sqrt{3}$


Correct Option: B
Explanation:

Clearly, one of $4^{\frac{1}{5}}$ and $5^{\frac{1}{4}}$ must be the smallest.
$\frac{1}{5}$<$\frac{1}{4}$.
So, $\displaystyle 4^{\frac{4}{20}}$ < $5^{\frac{5}{20}}$

Which of the following is the greatest?
$\sqrt{12}$, $\sqrt{13}$,$\sqrt{15}$,$\sqrt{17}$.

  1. $\sqrt{12}$

  2. $\sqrt{13}$

  3. $\sqrt{15}$

  4. $\sqrt{17}$


Correct Option: D
Explanation:

$12<13<15<17\ \Rightarrow \sqrt{12}<\sqrt{13}<\sqrt{15}<\sqrt{17}$

Therefore, $ \sqrt{17}$ is greatest.

Identify the irrational number(s) between $2\sqrt{3}$ and $3\sqrt{3}$

  1. $\sqrt{19}$

  2. $\sqrt{29}$

  3. $\cfrac { 4\sqrt { 3 } }{ \sqrt { 3 } } $

  4. $\sqrt{17}$


Correct Option: A,D
Explanation:
$2\sqrt{3}=\sqrt{12}$
$3\sqrt{3}=\sqrt{27}$
$\therefore \sqrt{176}\sqrt{19}$ are irrational no between them $\sqrt{29}$ lie out of it.
As $\dfrac{4\sqrt{3}}{\sqrt{3}}=4$ (Rational)

Compare the following pairs of surds. $\sqrt[4]{64}, \sqrt[6]{128}$    

  1. $\sqrt[4]{64} > \sqrt[6]{128}$

  2. $\sqrt[4]{64} < \sqrt[6]{128}$

  3. $\sqrt[4]{64} \neq \sqrt[6]{128}$

  4. $\sqrt[4]{64} = \sqrt[6]{128}$


Correct Option: A
Explanation:

$\sqrt[4]{64}=\sqrt[4]{2^6}=2\sqrt[4]{2^2}=2\sqrt{2}=2\sqrt[6]{2^3}=2\sqrt[6]{8}$
$\sqrt[6]{128}=\sqrt[6]{2^7}=2\sqrt[6]{2}$
$\sqrt[4]{64}>\sqrt[6]{128}$

The smallest of $\sqrt[3]{4},    \sqrt[4]{5},     \sqrt[4]{6},    \sqrt[3]{8}$ is:

  1. $\sqrt[3]{8}$

  2. $\sqrt[4]{5}$

  3. $\sqrt[3]{4}$

  4. $\sqrt[4]{6}$


Correct Option: B
Explanation:

(B) $\sqrt[3]{4}, \sqrt[4]{5},  \sqrt[4]{6}, \sqrt[3]{8}$

$=4^{1/3}, 5^{1/4}, 6^{1/4}, 8^{1/3}$

L.C.M of 3 & 4 $=12$

So, the given surds can be written as,

$=4^{4/12}, 5^{3/12}, 6^{3/12}, 8^{4/12}$

$=(4^{4})^{1/12}, (5^{3})^{1/12}, (6^{3})^{1/12}, (8^{4})^{1/12}$

$=(256)^{1/12}, (125)^{1/12}, (216)^{1/12}, (4096)^{1/12}$

$\therefore $ The smallest one is $\sqrt[4]{5}$

If $a = \sqrt {15} + \sqrt {11}, b = \sqrt {14} + \sqrt {12}$ then

  1. $a > b$

  2. $a < b$

  3. $a = b$

  4. None


Correct Option: B

$\sqrt{11}-\sqrt{10} .... \sqrt{12}-\sqrt{11}$,use appropriate inequality to fill the gap.

  1. <

  2. >

  3. $=$

  4. cannot determined


Correct Option: B
Explanation:

We first consider $\sqrt { 11 } -\sqrt { 10 }$ as follows:


$\sqrt { 11 } -\sqrt { 10 } =3.317-3.162=0.156$

Now we find the value of $\sqrt { 12 } -\sqrt { 11 }$ as follows:

$\sqrt { 12 } -\sqrt { 11 } =3.464-3.317=0.147$


Since $0.156>0.147$

Hence, $\sqrt { 11 } -\sqrt { 10 }>\sqrt {12} -\sqrt {11}$

If $p=\sqrt{32}-\sqrt{24}$ and $q=\sqrt{50}-\sqrt{48}$

  1. $p< q$

  2. $p> q$

  3. $p=q$

  4. $p\leq q$


Correct Option: B
Explanation:

(B) $\frac{p}{q}=\frac{\sqrt{32}-\sqrt{24}}{\sqrt{50}-\sqrt{48}}\times \frac{\sqrt{50}+\sqrt{48}}{\sqrt{50}+\sqrt{48}}$

$=\frac{(4\sqrt{2}-2\sqrt{6})(5\sqrt{2}+4\sqrt{3})}{2}$

$=(2\sqrt{2}-\sqrt{6})(5\sqrt{2}+4\sqrt{3})> 1$

$\therefore p> q$

If $x=\sqrt{2}+1,    y=\sqrt{17}-\sqrt{2}$, then:

  1. $x< y$

  2. $x > y$

  3. $x=y$

  4. $x\geq y$


Correct Option: A
Explanation:

(A) Given, $x=\sqrt{2}+1$ and $y=\sqrt{17}-\sqrt{2}$

$\dfrac{x}{y}=\dfrac{\sqrt{2}+1}{\sqrt{17}-\sqrt{2}}\times \dfrac{\sqrt{17}+\sqrt{2}}{\sqrt{17}+\sqrt{2}}$

$=\dfrac{(\sqrt{2}+1)(\sqrt{17}+\sqrt{2})}{17-2}$

$=\dfrac{(\sqrt{2}+1)(\sqrt{17}+\sqrt{2})}{15}< 1$

$\therefore x< y$

Arrange the following in ascending order of magnitude: $\displaystyle \sqrt[4]{90}, \sqrt[3]{10}, \sqrt{6}$

  1. $\displaystyle \sqrt{3} < \sqrt[4]{10} < \sqrt[3]{6}$

  2. $\displaystyle \sqrt{3} > \sqrt[4]{10} > \sqrt[3]{6}$

  3. $\displaystyle \sqrt{3} > \sqrt[4]{10} < \sqrt[3]{6}$

  4. $\displaystyle \sqrt{3} < \sqrt[4]{10} > \sqrt[3]{6}$


Correct Option: A

$if\,A\, = \sqrt 7  - \sqrt 6 \,and\,B = \,\sqrt 6  - \sqrt {5,} \,then\,$

  1. $A > B$

  2. $A = B$

  3. $A < B\,$

  4. $A \geqslant B$


Correct Option: C
Explanation:
Given numbers are $A=\sqrt{7}-\sqrt{6}$ and $B=\sqrt{6}- \sqrt{5}$
Let $x =\sqrt{5}$ and $y= \sqrt{7}$ then by
$A.M$ and $G.M$
$\dfrac{x+y}{2} \le \sqrt{\dfrac{x^{2}+y^{2}}{2}}$
$\Rightarrow \dfrac{\sqrt{5}+ \sqrt{7}}{2} \le \sqrt{6}$
$\Rightarrow \sqrt{5}+ \sqrt{7} \le 2 \sqrt{6}$
$\Rightarrow \sqrt{7}- \sqrt{6} \le \sqrt{6} - \sqrt{5}$

Which of the following numbers is the least ?
$\displaystyle (0.5)^{2},\sqrt{0.49},\sqrt[3]{0.008},0.23$

  1. $\displaystyle (0.5)^{2}$

  2. $\displaystyle \sqrt{0.49}$

  3. $\displaystyle \sqrt[3]{0.008}$

  4. 0.23


Correct Option: C
Explanation:

$ (0.5)^{2}=0.25$
$\sqrt{0.49}=0.7;$
$ \sqrt[3]{0.008}=\sqrt[3]{.2^3}=0.2$
$0.23$
Arranging in ascending order the numbers are $0.2< 0.23< 0.25< 0.7$
$ \therefore \sqrt[3]{0.008}=0.2$ is the least

The greatest number among $\displaystyle \sqrt[3]{2},\sqrt{3},\sqrt[3]{5}$ and $1.5$ is 

  1. $\displaystyle \sqrt[3]{2}$

  2. $\displaystyle \sqrt{3}$

  3. $\displaystyle \sqrt[3]{5}$

  4. $1.5$


Correct Option: B
Explanation:

LCM of $3, 2 = 6$
Given numbers are $ \sqrt[3]{2},\sqrt{3},\sqrt[3]{5}, 1.5$ i.e,
$ 2^{1/3},3^{1/2},5^{1/3},1.5$
$ \therefore $ Raising each number to power $6$, we get
$ (2^{1/3})^{6},(3^{1/2})^{6},(5^{1/3})^{6}, (1.5)^{6}$

$= 2^{2},3^{3},5^{2}, \left(\cfrac{3}{2}\right)^{6}$
$=4,27,25,\cfrac{729}{64}$
Of all these numbers, $27$ is the greatest.
$ \Rightarrow \sqrt{3}$ is the greatest. 

The smallest of $\displaystyle \sqrt{8}+\sqrt{5},\sqrt{7}+\sqrt{6},\sqrt{10}+\sqrt{3}$ and $\displaystyle \sqrt{11}+\sqrt{2}$ is 

  1. $\displaystyle \sqrt{8}+\sqrt{5}$

  2. $\displaystyle \sqrt{7}+\sqrt{6}$

  3. $\displaystyle \sqrt{10}+\sqrt{3}$

  4. $\displaystyle \sqrt{11}+\sqrt{2}$


Correct Option: D
Explanation:

$\displaystyle \sqrt{8}+\sqrt{5}=2.83+2.24=5.07$
$\displaystyle \sqrt{7}+\sqrt{6}=2.65+2.45=5.09$
$\displaystyle \sqrt{10}+\sqrt{13}=3.16+3.61=6.77$
$\displaystyle \sqrt{11}+\sqrt{12}=3.32+1.41=4.73$
$\displaystyle \therefore $ Smallest is $\displaystyle \sqrt{11}+\sqrt{2}$

Which one of the following set of surds is correct sequence of ascending order of their values?

  1. $\displaystyle \sqrt[4]{10},\sqrt[3]{6},\sqrt{3}$

  2. $\displaystyle \sqrt{3},\sqrt[4]{10},\sqrt[3]{6},$

  3. $\displaystyle \sqrt{3},\sqrt{10},\sqrt[3]{6},$

  4. $\displaystyle \sqrt[4]{10},\sqrt{3},\sqrt[3]{6}$


Correct Option: B
Explanation:

$\sqrt[4]{10},\sqrt[3]{6},\sqrt{3}$
The order of the given irrational numbers are 2,3,4.
LCM of (2,3,4)=12
Now convert each irrational number as of order 12
$\sqrt[4]{10}=\sqrt[12]{10^3}=\sqrt[12]{1000}$
$\sqrt[3]{6}=\sqrt[12]{6^4}=\sqrt[12]{1296}$
$\sqrt{3}=\sqrt[12]{3^6}=\sqrt[12]{729}$
Hence, ascending order$\sqrt{3}<\sqrt[4]{10}<\sqrt[3]{6}$

Which is the greatest out of the following ?

  1. $\displaystyle \sqrt[3]{1.728}$

  2. $\displaystyle \frac{\sqrt{3}-1}{\sqrt{3}+1}$

  3. $\displaystyle \left ( \frac{1}{2} \right )^{-2}$

  4. $\displaystyle \frac{17}{8}$


Correct Option: C
Explanation:
$\Rightarrow  \sqrt[3]{1.728}=1.2$

$\Rightarrow \cfrac{\sqrt{3}-1}{\sqrt{3}+1}=\cfrac{(\sqrt{3}-1)^{2}}{(\sqrt{3}+1)(\sqrt{3}-1)}=\cfrac{3+1-2\sqrt{3}}{3-1}$
$ =\cfrac{4-2\sqrt{3}}{2}=2-\sqrt{3}$
$ =2-1.732=0.268$

$\Rightarrow \left ( \cfrac{1}{2} \right )^{-2}=2^{2}=4$

$\Rightarrow \cfrac{17}{8}=2.2125$

$ \therefore \left ( \cfrac{1}{2} \right )^{-2}$ is the greatest. 

$4\sqrt{18}$ $=$ $12\sqrt{2}$
State true or false

  1. True

  2. False


Correct Option: A
Explanation:

Consider $4\sqrt { 18 }$ and factorize it as follows:

 
$4\sqrt { 18 } =4\sqrt { 2\times 3\times 3 } =4\sqrt { 2\times 3^{ 2 } } =4\times 3\sqrt { 2 } =12\sqrt { 2 }$
 
Hence, $4\sqrt { 18 } =12\sqrt { 2 }$    

Which is greater $\displaystyle (\sqrt{7}+\sqrt{10})$ or $\displaystyle (\sqrt{3}+\sqrt{19})$?

  1. $\displaystyle \sqrt{7}+\sqrt{10}$

  2. $\displaystyle \sqrt{3}+\sqrt{19}$

  3. Both are equal

  4. None of these


Correct Option: B
Explanation:

$(\sqrt{7}+\sqrt{10})$
$2.6457+3.1622=5.8079$
$(\sqrt{3}+\sqrt{19})$
$1.732+4.358=6.090$
Hence $(\sqrt{3}+\sqrt{19})$is greater.

$\displaystyle \sqrt[4]{3},\sqrt[6]{10},\sqrt[12]{25}$, when arranged in descending order will be 

  1. $\displaystyle \sqrt[4]{3},\sqrt[6]{10},\sqrt[12]{25}$

  2. $\displaystyle \sqrt[6]{10},\sqrt[4]{3},\sqrt[12]{25}$

  3. $\displaystyle \sqrt[6]{10},\sqrt[12]{25},\sqrt[4]{3}$

  4. $\displaystyle \sqrt[4]{3},\sqrt[12]{25},\sqrt[6]{10}$


Correct Option: B
Explanation:

LCM of $4, 6$ and $12 = 12$.
$ \therefore $ Raising each of the given number to power $12$, we have 
$ (3^{1/4})^{12},(10^{1/6})^{12},(25^{1/12})^{12}$
$= 3^{3},10^{2},25$
$= 27, 100, 25$
Arranging in descending order, the numbers are $ 100, 27, 25$
$\Rightarrow \sqrt[6]{10},\sqrt[4]{3},\sqrt[12]{25}$

The greatest amongst the the values $0.7 + \sqrt { 0.16 } ,  1.02 - \displaystyle\frac { 0.6 }{ 24 } ,   1.2 \times 0.83$ and $\sqrt { 1.44 } $ is

  1. $0.7+\sqrt { 0.16 } $

  2. $1.02-\displaystyle\frac { 0.6 }{ 24 } $

  3. $1.2\times 0.83$

  4. $\sqrt { 1.44 } $


Correct Option: D
Explanation:

$0.7+ \sqrt { 0.16 } = 0.7 +0.4 = 1.1$ 

$1.02-\displaystyle  \frac { 0.6 }{ 24 } = 1.02 - 0.025 = 1.175$
$1.2 \times 0.83 = 0.996 $
$\sqrt { 1.44 } = 1.2$

$\therefore $ the greatest is $\sqrt { 1.44 } $.

Which of the following is smallest?

  1. $\sqrt [4]{5}$

  2. $\sqrt [5]{4}$

  3. $\sqrt {4}$

  4. $\sqrt {3}$


Correct Option: B
Explanation:

Let us rewrite the given set of magnitudes $\sqrt [ 4 ]{ 5 } ,\sqrt [ 5 ]{ 4 } ,\sqrt { 4 },\sqrt {3}$ as follows:


$\sqrt [ 4 ]{ 5 } ={ \left( 5 \right)  }^{ \dfrac { 1 }{ 4 }  }\ \sqrt [ 5 ]{ 4 } ={ \left( 4 \right)  }^{ \dfrac { 1 }{ 5 }  }\ \sqrt { 4 } ={ \left( 4 \right)  }^{ \dfrac { 1 }{ 2 }  }\ \sqrt { 3 } ={ \left( 3 \right)  }^{ \dfrac { 1 }{ 2 }  }$

 
We now take the LCM of the denominators of the powers to make the denominators same, then the above magnitudes will be:

$\sqrt [ 4 ]{ 5 } ={ \left( 5 \right)  }^{ \dfrac { 1\times 5 }{ 4\times 5 }  }={ \left( 5 \right)  }^{ \dfrac { 5 }{ 20 }  }={ \left( { 5 }^{ 5 } \right)  }^{ \dfrac { 1 }{ 20 }  }={ \left( 3125 \right)  }^{ \dfrac { 1 }{ 20 }  }=\sqrt [ 20 ]{ 3125 } \\ \sqrt [ 5 ]{ 4 } ={ \left( 4 \right)  }^{ \dfrac { 1\times 4 }{ 5\times 4 }  }={ \left( 4 \right)  }^{ \dfrac { 4 }{ 20 }  }={ \left( { 4 }^{ 4 } \right)  }^{ \dfrac { 1 }{ 20 }  }={ \left( 256 \right)  }^{ \dfrac { 1 }{ 20 }  }=\sqrt [ 20 ]{ 256 } \\ \sqrt { 4 } ={ \left( 4 \right)  }^{ \dfrac { 1\times 10 }{ 2\times 10 }  }={ \left( 4 \right)  }^{ \dfrac { 10 }{ 20 }  }={ \left( { 4 }^{ 10 } \right)  }^{ \dfrac { 1 }{ 20 }  }={ \left( 1048576 \right)  }^{ \dfrac { 1 }{ 20 }  }=\sqrt [ 20 ]{ 1048576 } \\ \sqrt { 3 } ={ \left( 3 \right)  }^{ \dfrac { 1\times 10 }{ 2\times 10 }  }={ \left( 3 \right)  }^{ \dfrac { 10 }{ 20 }  }={ \left( { 3 }^{ 10 } \right)  }^{ \dfrac { 1 }{ 20 }  }={ \left( 2187 \right)  }^{ \dfrac { 1 }{ 20 }  }=\sqrt [ 20 ]{ 2187 }$     

Now, the descending order is as shown below:

$\sqrt [ 20 ]{ 1048576 } >\sqrt [ 20 ]{ 3125 } >\sqrt [ 20 ]{ 2187 } >\sqrt [ 20 ]{ 256 } \\ \Rightarrow \sqrt { 4 } >\sqrt [ 4 ]{ 5 } >\sqrt { 3 } >\sqrt [ 5 ]{ 4 }$ 

Hence, the smallest magnitude is $\sqrt [ 5 ]{ 4 }$.

Arrange the following surds in ascending order of their magnitudes: $\sqrt{5},\sqrt [ 3 ]{ 11 } ,2\sqrt [ 6 ]{ 3 } $

  1. $\sqrt [ 3 ]{ 11 } > \sqrt{5}< 2\sqrt [ 6 ]{ 3 } $

  2. $\sqrt [ 3 ]{ 11 } < \sqrt{5}< 2\sqrt [ 6 ]{ 3 } $

  3. $\sqrt [ 3 ]{ 11 } > \sqrt{5}> 2\sqrt [ 6 ]{ 3 } $

  4. $\sqrt [ 3 ]{ 11 } < \sqrt{5}> 2\sqrt [ 6 ]{ 3 } $


Correct Option: B
Explanation:

$\sqrt{5} = 5^{1/2}$

$\sqrt[3]{11} = 11^{1/3}$

$2\sqrt[6]{3} = \sqrt[6]{12}= 12^{1/6}$

L.C.M of the denominators of the exponents is 12.

So,

$\sqrt{5} = 5^{\frac{1}{2}\times\frac{6}{6}} = \sqrt [12]{5^6}=\sqrt[12]{15625}$

$\sqrt[3]{11} = 11^{\frac{1}{3}\times\frac{4}{4}} = \sqrt [12]{11^4} =\sqrt[12]{14641}$

$2\sqrt[6]{3} = \sqrt[6]{12}= 12^{\frac{1}{6}\times\frac{2}{2}} = \sqrt[12]{12^2} =\sqrt[12]{144}$

Hence, the Ascending order is $2\sqrt[6]{3}, \sqrt[3]{11},\sqrt{5}$

Write $\displaystyle \sqrt[4]{6},\sqrt{2},\sqrt[3]{4}$ in ascending order

  1. $\displaystyle \sqrt{2},\sqrt[4]{6}$ and $\displaystyle \sqrt[3]{4}$

  2. $\displaystyle \sqrt[4]{6}$, $\sqrt{2}$ and $\displaystyle \sqrt[3]{4}$

  3. $\displaystyle \sqrt{2}$, $\displaystyle \sqrt[3]{4}$ and $\sqrt[4]{6}$

  4. None of these


Correct Option: A
Explanation:

$\displaystyle 6^\cfrac 14,2^\cfrac 12,4^\cfrac 13$
The surds are of the order $4, 2$ and $3$ respectively The L.C.M. is $12$ So, we change each surd of the order $12$
The terms now are $\displaystyle \left ( 6^{3} \right )^\cfrac {1}{12},\left ( 2^{6} \right )^\cfrac{1}{12}$ and $\displaystyle \left ( 4^{4} \right )^\cfrac{1}{12}$
$\displaystyle \Rightarrow \left ( 216 \right )^\cfrac{1}{12},\left ( 64 \right )^\cfrac{1}{12}$ and $\displaystyle \left ( 256 \right )^\cfrac{1}{12}$
$\displaystyle \therefore $ Ascending order is $\displaystyle \sqrt{2},\sqrt[4]{6}$ and $\displaystyle \sqrt[3]{4}$

State true or false
$\sqrt { 17 } -\sqrt { 12 } $ is less than $\sqrt { 11 } -\sqrt { 6 } $

  1. True

  2. False


Correct Option: A

State true or false 

$\sqrt { 7 } -\sqrt { 3 } $ is greater than $\sqrt { 5 } -1$ 

  1. True

  2. False


Correct Option: B

Which is greater?
${ \left( \cfrac { 1 }{ 2 }  \right)  }^{ 1/2 } $ or ${ \left( \cfrac { 2 }{ 3 }  \right)  }^{ 1/3 } $

  1. ${ \left( \cfrac { 2 }{ 3 }  \right)  }^{ 1/3 } $

  2. ${ \left( \cfrac { 1 }{ 2 }  \right)  }^{ 1/2 } $

  3. Both are equal

  4. None of the above


Correct Option: A
Explanation:

$ \left(\dfrac{1}{2}\right)^{1/2} \; or \; \left(\dfrac{2}{3}\right)^{1/3}$


$= \left(\left(\dfrac{1}{2}\right)^{1/2}\right)^6 \; or \; \left(\left(\dfrac{2}{3}\right)^{1/3}\right)^6$


$= \left(\dfrac{1}{2}\right)^3 \; or \; \left(\dfrac{2}{3}\right)^2$


$= \left(\dfrac{1}{8}\right) \; or \; \left(\dfrac{4}{9}\right)$


= 0.125 or 0.44


Since, 0.44 is greater and so is $ \left(\dfrac{2}{3}\right)^{1/3}$

The correct descending order of the following surds is 

$ \sqrt [3]{2}$, $\sqrt 3$, $\sqrt 4$, $\sqrt 5$

  1. $\sqrt 3$ > $\sqrt 4$ > $\sqrt 5$ > $\sqrt [3]{2}$

  2. $\sqrt 4$ > $\sqrt 5$ > $\sqrt [3]{2}$ > $\sqrt 3$

  3. $\sqrt 5$ > $\sqrt 4$ > $\sqrt 3$ > $\sqrt [3]{2}$

  4. $\sqrt [3]{2}$ > $\sqrt 4$ > $\sqrt 3$ > $\sqrt 5$


Correct Option: C
Explanation:

LCM of $3$ and $2$ is $6$.
Therefore, multiplying the index of all numbers by $6$.
${\sqrt [3]{2}}^6 = 2^\dfrac 63 = 2^2 = 4$

${\sqrt 3}^6 = 3^\dfrac 62 = 3^3 = 27$

${\sqrt 4}^6 = 4^ \dfrac 62 = 4^3 = 64$

${\sqrt 5}^6 = 5^{\dfrac 62} =  5^3 = 125$

$\therefore 125 > 64 > 27 > 4$

So, option $C$ is correct.

Which one of the following is an irrational number?

  1. $\sqrt[3]{-27}$

  2. $\sqrt{2}(3\sqrt{2}+2\sqrt{8})$

  3. $\dfrac{3\sqrt{18}}{2\sqrt{6}}$

  4. $\sqrt{\dfrac{1}{2}}\cdot\sqrt{\dfrac{25}{2}}$

  5. $\dfrac{2\sqrt{5}}{\sqrt{45}}$


Correct Option: C
Explanation:

Option A: $\sqrt [ 3 ]{ -27 } ={ (-3) }^{ 3\times \frac { 1 }{ 3 }  }=-3$
Option B: $\sqrt { 2 } (3\sqrt { 2 } +2\sqrt { 8 } )=\sqrt { 2 } (3\sqrt { 2 } +4\sqrt { 2 } )=\sqrt { 2 } (7\sqrt { 2 } )=14$
Option C: $\dfrac { 3\sqrt { 18 }  }{ 2\sqrt { 6 }  } =\dfrac { 3\sqrt { 3 }  }{ 2 } $
Option D: $\sqrt { \dfrac { 1 }{ 2 }  } \sqrt { \dfrac { 25 }{ 2 }  } =\dfrac { 5 }{ 2 } $
Option E: $\dfrac { 2\sqrt { 5 }  }{ \sqrt { 45 }  } =\dfrac { 2\sqrt { 5 }  }{ 3\sqrt { 5 }  } =\dfrac { 2 }{ 3 } $
Therefore, all are rational except option $C$.

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